Quarantine Sucks, but gives us all more time to read
Since everyone has more time to read right now, I thought I'd give you a list of reading sites that I know of. (Going through my bookmarks and finding out how many sites no longer exist was actually pretty sad.)
https://www.fanfiction.net/ is the main one of course, it carries nearly everything, but that's not the only site that is available. (They also have another site that everyone forgets about for original fiction https://www.fictionpress.com/)
https://archiveofourown.org/ is similar to FF.net and gets every fic that FF.net doesn't like the looks of. Consider that fair warning for what you'll find there.
https://www.tthfanfic.org/ is a favorite of mine, primarily focusing on BtVS crossover fanfiction. It's a great site and I love it.
https://www.fanficauthors.net/ a very nice site, developed to hold Jeconais' stories and expanded to house a dozen high quality fanfiction authors. The authors don't update all that often as they have mostly moved on from fanfiction, in fact two of them became professional authors that I know of.
http://www.angelfire.com/anime5/fanficlair/ is the personal site of Black Dragon and he wrote some epic, hilarious, insane Ranma 1/2 fanfics. https://www.fanfiction.net/u/198979/Black-Dragon6 is his FF.net page, but his personal site had some things it doesn't.
adult-fanfiction.org is a site that focuses on stuff you can't post on other sites and some authors use alternate IDs to post works they don't want to link to their main account there. *whistles innocently*
https://www.phoenixsong.net/ is a Harry Potter site and has few updates these days but they have a large amount of stories. http://www.fictionalley.org/authors/ is much the same.
http://www.hpfanficarchive.com/ is another HP site, but this one specializes in mature HP fanfiction. Consider yourself warned.
https://www.fimfiction.net/ everything pony... seriously everything! When I say they have everything, I mean that any possible story involving ponies exists there. Abandon all Hope...
https://ficwad.com/ An old site covering a load of Fandoms. It was AO3 before AO3 existed. Surprisingly it's still alive, but often plagued with spammers.
https://www.mediaminer.org/ is also still alive, but barely and has a large amount of anime fanfiction that was deleted from other sites over the years.
http://www.florestica.com/ is a classic site with some of the best anime fanfiction written during the 80's and 90's. Hasn't been updated in forever!
http://www.fukufics.com is a specialty site that only covers Ranma 1/2 Sailor Moon crossovers.
https://fanficaddventure.7thpylon.com/ is a mirror of Bast's Addventure Board where a lot of us posted, until it finally crashed and the admins vanished. It's basically CYOA and the quality and rating is completely random, but I had a lot of fun posting there as did some other excellent authors.
http://old.bearchive.com/~addventure/game1/trees/index.html This is the closest thing to Bast's site that is still online. There are a few good authors writing some decent threads there, but you have to search to find them.
http://t-s-s-a.com/ Nothing but mature stories of TV shows and cartoons. Still running strong and covers a wide range of shows. People are reallllly strange.
http://stfan.free.fr/ Ranma 1/2 Lemon archive hasn't been updated since 2009 but that means it archived all the Ranma material available during it's boom.
http://xanderzone.osiris-web.com/ a mirror of the Xanderzone after it died with the site administrator Grandt. If you like Xander (and since you read my stuff you probably do) then you will like this site, even tho the stories on it are never going to be updated here.
http://jv.osiris-web.com/ The Journeyverse... the most epic Xander roadtrip story ever. At least a dozen authors got involved and it is massive! I tend to lose a week or two when I run across it because I love rereading it.
Hopefully that gives everyone a decent amount of new things to read.